Solid state NMR and X-ray diffraction study of three forms of the aluminophosphate AlPO 4-ZON

Abstract

As-synthesized, calcined and calcined-rehydrated AlPO 4- ZON materials have been studied using powder XRD and multinuclear solid state NMR techniques. A new assignment for the four 31P signals of the as-synthesized sample is presented. A Rietveld refinement on synchrotron data allows to elucidate the structure of the calcined material. Although the space group (Pbca) and the framework topology are similar to those of the previously studied as-synthesized and calcined-rehydrated materials, all four Al sites now exhibit a fourfold coordination. This is in agreement with the result of an 27Al 5QMAS NMR experiment. Furthermore, the bond distances deduced from this structural refinement, combined with a 31P homonuclear correlation experiment, allow assignment of the 31P resonances. Only a partial assignment of the 27Al signals could be achieved for the rehydrated material.